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[Linphone-developers] Echo on calls with linphone apk on zebra devices

From: Cosmina Nicolau
Subject: [Linphone-developers] Echo on calls with linphone apk on zebra devices
Date: Tue, 21 Dec 2021 13:59:25 +0100

Hello everybody,

Before discussing the problem I have, I will describe the scenario what I am working on: there are 4 android devices model Zebra TC21. These devices behave as SIP client against the server (PBX) for call management system implemented on the server and managed by asterisk.

We are developing or own application based on linphone sdk to manage those communications, but when we try to make a call between two mobile devices, we have issues with echo during the phone call.

For this reason we have started to test only with linphone's own application (V.4.5.6 // SDK 5.0.49) to verify or exlude that the problem is derived from the linphone's sdk, and, in fact, we still have the same problem, when we try to make a call between two devices we hear a annoying echo and it always happens when is a TC21 device involved.

Another of the tests carried out was to install the linphone application on personal Android devices (specifically a Xiaomi Redmi Note 9s pro  with Android 11 and OnePlus T5 with Android 10) and the expected behavior is correct, there is no echo feeling.

The most relevant settings in the linphone application are the following (on audio settings) :
  • Enabled echo cancellation.
  • Enabled adaptive rate control.
  • The only codec enabled is g722.
  • Microphone gain is set to 0 and playback gain also is set to the same value,

We don't know if the problem is associated with the linphone sdk or in particular, with the TC21 model device, since tests have also been performed wtih TC20 device and there is no echo feedback. How do we avoid the echo during calls?

On the other hand, I have also requested support from Zebra describing the same problem to get support from them as well, but I need to confirm on this side that it is not produced due to a problem with the linphone sdk.


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